Controversy has existed regarding the relative merits of preserving regional lymph nodes with respect to their immunological role in the current management of breast cancer. However, no studies have been done to date regarding the immunological status of axillary lymph nodes (ipsilateral and contralateral) to specific breast tumor antigen. Studies are planned to determine by in vitro cellular techniques the immunocompetence of regional lymph nodes and contralateral axillary lymph nodes to breast tumor antigen. Their immunological reactivity will be compared to peripheral blood lymphocytes to determine if there exists any significant difference in the immunological status of these three populations of lymphocytes. Lymphocytes will be obtained from lymph nodes at the time of radical mastectomy and tested against breast tumor cells and breast tumor extract obtained from the same patient. Cellular reactivity will be measured utilizing the direct migration inhibition technique and blastogenic transformation as measured by radioactive uptake of tritiated thymidine. Mixed lymphocyte culture of patients' lymph node lymphocytes and peripheral blood lymphocytes will be performed to determine if there is any antigenic difference in the lymph node cells because of possible entrapment of breast tumor cells. All patients studied will be followed over the course of two years to determine any alteration in their immunological statis in relation to possible adjuvant therapy. Patients having four or more lymph nodes involved with tumor will be compared to patients having no lymph node involvement to determine if the poor prognosis seen with patients with nodal involvement is related to deficiencies in immunological reactivity. Hopefully, this information will help clarify the current controversy regarding treatment of patients having breast cancer: radical mastectomy versus simple mastectomy.